Think you've seen the worst that mad science has to offer? How about an experiment in which scientists rendered kittens essentially sightless? And that's not the worst of it. Learn about harnessed kittens, yoked kittens, kittens going over a visual cliff, and researchers fake-punching a kitten.

How do you virtually blind someone without doing any damage to their eyes? These are the kinds of questions that continually plague the evil. Lucky for you, scientists have figured it out. And just to be extra poignant, they figured it out using kittens. In what's known as the "two kitten experiment," we learned how to make eyes useless.

The Set-Up

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The set-up for this experiment involved ten litters of kittens. The litters were born, and for the first few weeks, raised in darkness. One pair was selected from each litter. Of the pair, one kitten was selected to be the Mobile Kitten, and one to be the Immobile Kitten. Both kittens were taken away from their litters for a time and placed on a kind of turntable called the kitten carousel.

The Mobile Kitten was placed in a harness, and allowed to move around the turntable. The Immobile Kitten was put in a basket with its head sticking out. Since the kittens were yoked together, the Immobile Kitten was moved in whichever way the Mobile Kitten moved. Part of the bottom of its basket was even removed, so it could feel its paws dragging on the ground. It just couldn't initiate any movement. After some time, the kittens were taken off the turntable and returned to the dark room with their littermates.

The Results

After a few sessions, the kitten pairs were given a series of tests. The kittens were taken to lighted rooms. The experimenters slowly lowered them toward a table. The Mobile Kitten stretched out its paws, in anticipation of touching the surface it saw approaching. The Immobile Kitten did not. They put the kittens on what's known as a visual cliff.

Visual cliffs are surfaces that are level on one side but drop suddenly away on the other, like the deep end of a swimming pool. The entire structures are completely covered by a layer of plastic, so no one walking on them can actually fall. They just look scary. The Mobile Kitten avoided the "deep" end of the visual cliff. The Immobile Kitten did not.

The scientists finished off with what's known as the blink test. Holding the kittens still, one researcher quickly brought one hand close to the kitten's face - but didn't actually hit it. The Mobile Kitten blinked, anticipating a hit. The Immobile Kitten did not blink.

Both kitten had been exposed to exactly the same factors growing up. When they were harnessed, they moved in the same way and were given the same tactile stimulus. All that differed between one kitten and the other was the ability to initiate the movement. That was enough. Without the ability to somehow affect the things it was looking at, the Immobile Kitten wasn't able to connect the movement with any meaning. Although it could see, it was functionally blind.

The experiment has a somewhat happy ending. The Immobile Kittens were placed in lighted rooms for about forty-eight hours and allowed to explore freely. They were retested and had learned to understand visual cliffs. So even if deprived of stimulus, the brain can still learn. Still, the Immobile Kittens never became visually normal. Their time in the dark, and without the ability to work with the world around them, left a permanent mark on them.